Gas blast circuit breaker with noisereducing exhaust muffler assembly



May 26, 1964 HANG 3 134,876

H. C ETAL 9 GAS BLAST CIRCUIT BREAKER WITH NOISE-REDUCING" EXHAUSTMUFFLER ASSEMBLY Filed Oct. 2. 1961 2 Sheets-Sheet 1 FIG.

INVENTORS. HAN CHANG, V/NCE/VT/V. STEWART,

5y UM 2am ATTORNEY.

May 26, 1964 H. CHANG ETAL GAS BLAST CIRCUI 3,134,876 T BREAKER WITHNOISE-REDUCING EXHAUST MUFFLER ASSEMBLY 2 Sheets-Sheet 2 Filed Oct. 2,1961 INVENTORS. HAN CHANG, V/NCfNT N. STEWARZ ATTORNEY.

United States Patent GAS BLAST CIRCUIT BREAKER WITH NGiSE- REDUCINGEXHAUST MUFFLER ASSEMBLY Han Chang, Brookhaven, and Vincent N. Stewart,Springfield, Pa., assignors to General Electric Company, a corporationof New York Filed (let. 2, 1961, Ser. No. 142,338 9 Claims. (Cl.200-448) The present invention relates to a gas blast type of electriccircuit breaker and, more particularly, relates to a mufller assemblyfor reducing the noises resulting from the flow of hot exhaust gasesfrom the circuit breaker to the surrounding atmosphere.

In a gas-blast type of circuit breaker, circuit interruption is effectedby causing a high speed blast of pressurized gas to flow for a shortperiod through the usual arcing region of the breaker. This blastfacilitates circuit interruption by cooling the arc and by cleansing thearcing region of hot metallic vapors and other highly heated arcingproducts. Upon leaving the arcing region, the highly heated gases aredischarged to the surrounding atmosphere in a short and intense burst.In most prior gas blast circuit breakers, the heated gases are thenflowing at high speed, and the result is a loud noise, which in manycases is objectionable.

An object of our invention is to provide an improved exhaust mufilerthat is capable of greatly reducing the amount of noise resulting fromoperation of the circuit breaker. Another object is to provide a mufllerof this nature which is highly compact and does not create anobjectionable amount of back pressure that could impair the ability ofthe gas blast to perform its intended arc-extinguishing function.

Another object is to provide a mufller, which although compact andefiicient in reducing noise, allows gases to be dissipated therefromrapidly enough to permit 'an unimpeded, closely-succeeding operation ofthe circuit breaker.

In the mufller of our invention, the exhaust gases are introduced into achamber from which they are discharged in a controlled manner through alarge number of spacedapart openings in the walls of the chamber.Another object of our invention is to distribute this flow. generallyuniformlybetween substantially all these openings so that excessivevelocities donot occur through the openings in any localized region ofthe muffler.

In carrying out our invention in one form, we provide in a gas blastcircuit breaker having an exhaust passage through which pressurizedgases are exhausted after flowing through the arcing region of thecircuit breaker, an exhaust muffler comprising a pair of end walls and ahollow enclosure extending axially of the muffier betweenthe end wallsto define a chamber internally thereof. The enclosure has perforationsextending generally radially therethrough at spaced-apart locationsabout substantially its entire periphery and length for allowing exhaustgases to flow generally radially outward therethrough. In one of the endwalls there is provided an inlet to the expansion chamber thatcommunicates with the exhaust passage for directing exhaust gasesaxially of the mufiler towards said other end wall. Within the chamberthere is provided means including a deflector on said other end wall forcausing gases from the inlet to flow in a reverse axial direction alongthe internal wall of the enclosure after impinging against thedeflector. This reverse axial flow helps to provide a more uniformdistribution of flow through the perforations in the enclosure.

While the specification concludes with claims particularly pointing outand distinctly claiming the subject mat- 3,134,876 Patented May 26, 1964ter which may be regarded as the invention, the organization and methodof operation, together with further objects and advantages thereof, maybest be understood by reference to the following description taken inconnection with the accompanying drawings in which:

FIG. 1 is a partially schematic side elevational view of a circuitbreaker embodying one form of the present invention; and

FIG. 2 is an enlarged sectional view along the line 2-2 of FIG. 1.

Referring to the drawings and particularly to FIG. 1, the circuitbreaker shown therein comprises a metallic tank 10 mounted upon a hollowinsulating column 11 with an exhaust mufiler assembly 9 of the presentinvention therebetween. The tank is at a high voltage with respect toground, and the insulating column 11 serves to electrically isolate thetank from ground as well as to support the tank. The tank 10 is normallyfilled with pressurized gas that serves as an arc-extinguishing mediumas will hereinafter be described. The basic circuit breaker structureWithin the tank generally corresponds to that disclosed in detail andclaimed in U.S. Patent No. 2,783,338Beatty, assigned to the assignee ofthe present invention. The structure of the circuit breaker will bedescribed herein only to the extent believed necessary to convey anunderstanding of the present invention that relates to the exhaustmufiler assembly. Reference may be had to the Beatty patent if a moredetailed description is desired of the circuit breaker.

Referring now to the structure within the tank 10, there are two pairsof contacts disposed therein. One pair of contacts comprises astationary contact 12 and a movable contact 14. The other pair ofcontacts comprises a stationary contact 13 and a movable contact 15. Themovable contacts 14 and 15 are mounted on two stationary pivots 16 and17 carried by a central metallic support 20 that is mechanically andelectrically connected tothe tank 10. The stationary contact 12 is shownmounted on the inner end of a lead-in bushing 25 projecting into thetank through its left-hand end wall and providing anelectricalconnection through a conductive stud 27 between the stationarycontact 12 and a terminal 29 of the circuit breaker. The otherstationary contact 13 is shown mounted on a bushing 26 projecting intothe tank through its right-hand end wall and providing a connectionthrough a conductive stud 28 between the other terminal 30 of thecircuit breaker and the contact 13. The lead-in bushings 25 and 26insulate the contacts 12 and 13 from. the tank 10 when the circuitbreaker is open.

For imparting opening or closing motion to the movable contacts 14 and15, a common driving member in the form of a reciprocal crosshead 35 isprovided. The movable contact 14 is coupled to this crosshead 35 bymeans of a link 36 pivotally connected at its respective opposite endsto the crosshead 35 and the movable contact 14, whereas the movablecontact 15 is coupled to the crosshead 35 by means of a second link 37pivotally connected at its respective opposite ends to the crosshead 35and the movable contact 15. Upward movement of the crosshead 35 causesthe lower ends of the movable contacts 14 and 15 to separate from theirrespective stationary contacts 12 and 13, and move into an openposition; whereas return movement of the cross head 35 returns themovable contacts 14 and 15 from the open position to a closed position.

present invention and therefore will not be described in thisapplication. Preferably, however, the operating mechanism is of the typedisclosed and claimed in the aforementioned Beatty'Patent 2,783,338.

For extinguishing the arcs formed between the contacts upon opening ofthe circuit breaker, a blast of pressurized air is caused to flowthrough the arcing region. This blast of air is controlled by anormally-closed blast valve 38 mounted within the metallic support 20.When the blast valve 38 is lifted into its open position, communicationis established between an exhaust passage 40 and the space within thetank through exhaust orifices 39. This causes pressurized gas within thetank to flow through the arcing region into the exhaust passage 40 viapaths generally indicated by the dotted line arrows 41 of FIG. 1. Whencircuit interruption is completed, the blast valve is returned to itsclosed position to terminate the gas blast. The blast valveand itscontrol means are described in greater detail in the aforementionedBeatty patent. The gases flowing through the exhaust passage 40 areextremely hot inasmuch as they consist of arcing products or gases thathave been heated by the arc. After passing through the exhaust passage40, these hot gases enter the muflier assembly 9, from which they aredischarged to the surrounding atmosphere in a manner which will soon bedescribed in more detail.

Referring now to FIG. 2, a sectional view along the line 2-2 of FIG. 1is shown of the exhaust muffler assembly 9. Upper and lower parallelplates 45 and 46 which are perpendicular to the axis of the exhaustpassage 40 are arranged to receive suitable tie bolts therethrough suchas shown at 47 to clamp therebetween the respective elements that formthe improved exhaust muffler assembly of the present invention. Theupper plate 45 has a suitable central aperture 48 aligned with theexhaust passage 40 from the pressurized tank 10 of FIG. 1. An upperdeflector 50 is secured to the upper plate 45 by a plurality of boltssuch as shown at 53. The upper deflector has a centrally-locatedaperture 52 aligned with the exhaust passage 40 and a downwardly openingconcave face51 that surrounds the central aperture 52. A thin-walledring 54 fits within the central aperture 52 in the upper deflector 50.The aligned apertures 48 and 52 and the ring 54 together define an inletto the muffler assembly 9. Opposing the upper deflector 50 and spacedtherefrom is a lower deflector 55 having an active surface 56 of agenerally semi-toroidal form. Interposed between the lower deflector 55and the lower plate 46 is a resilient buffer member 60 of rubber or thelike secured to the lower plate 46 by a plurality of bolts, such asshown at 61, whereeach bolt has a resilient washer 62 disposed betweenits head and the lower deflector 55 to substantially isolate the lowerdeflector 55 from direct contact with the lower plate 46 of theassembly; Preferably, a thrust plate such as shown at 63 is positionedbetween the lower deflector 56 and the buffer 60 to more uniformlydistribute the downward force transmitted to the buffer 60, as will soonappear more clearly.

The upper plate 45 and the lower plate 46 retain in a sandwich form aplurality of concentric cylinders 65-68 therebetween. These cylindersmay be thought of as constituting a hollow enclosure for an expansionchamber 69 disposed internally thereof. The perforated cylinders 65 and66 are radially spaced from each other to define a suitable acousticchamber 70 therebetween. Suitable spacers 71 disposed between these twocylinders assure that'the desired spacing is maintained. The innercylinder 65 is provided with a plurality of perforations such as at 75distributed over substantially its entire periphery and length. Theintermediate or second cylinder 66 is also suitably perforated such asat 76, preferably with an increased total number of perforations havinga reduced diameter as compared to those provided in the first cylinder65. 'These perforations 76 are distributed over a major portion of theperiphery and length of the cylinder 66. Exhaust gases from theexpansion chamber 69 will be discharged radially outward through theperforations in the two cylinders 65 and 66. Gases passing through theperforated second cylinder 66 will impinge upon a porous cylinderassembly 67 that is preferably formed, in accordance with one form ofthe present invention, of three distinct elements comprising thecylindrical reticulated members, or screens, 77 and 78 and a compactedfiller 79 therebetween of copper wool or a similar substance thatretains a porous quality when suitably compacted. The porous cylinderassembly 67 thus formed, further restricts the escaping exhaust gasesthat pass through the second perforated cylinder 66 and attenuates highfrequency noise. In the form of the invention being described, anexterior porous cylinder 68 is positioned as shown adjacent to theperiphery of the porous cylinder assembly 67 and may be formed from aporous material, such as loosely-woven cellulose fibers, to furtherattenuate noise. A plurality of vertically-spaced louvers 85, each of agenerally annular form with a downwardly flared periphery, are shownpositioned adjacent to but spaced from the periphery of the outercylinder 68 to provide the mutlier assembly with adequate protectionagainst possible contamination from moisture. Where moisturecontamination is no problem, the louvers may be omitted.

Again referring particularly to FIG. 2, the operation of the exhaustmnfiier assembly 9 formed in accordance with the present inventionprovides that the hot exhaust gases released from the pressurized tank10, shown by FIG. 1, will enter the exhaust muffler assembly 9 throughthe exhaust passage 40 and the muflier inlet 48, 52. The hot exhaustgases then flow axially of the muflier assembly in a downward directionand impinge directly upon the lower deflector 55, which reverses thedirection of flow of the exhaust gases to a new direction that isgenerally opposed to the entrance flow of the exhaust gases. A portionof the exhaust gases will thereafter impinge upon the upper deflector50, and this results in flow again being reversed by approximately 180from the previous direction. This path followed by the hot exhaust gasesas their direction of flow is reversed by the deflectors is generallyindicated by the dotted line arrows 88 of FIG. 2. While some of theexhaust gases are flowingrepetitively over this dotted line path, someare also exhausting radially outward through the perforations of theinner cylinder 65 after traversing only a portion of this path.

The buffer member 60 in the present invention provides a substantialreduction in the noise and vibration that results from the sharp impactcaused by the sudden axial flow of the exhaust gases into the exhaustmuffler assembly 9 when the circuit breaker is opened. For example,

in some circuit breakers, this sudden flow of exhaust gases produces aforce of approximately 2000 pounds inasmuch as the escape velocity ofthe exhaust gases into the muffler assembly is 600 or 700 feet persecond. By absorbing a substantial portion of this impact energy insteadof allowing it to be transmitted directly to the lower metallic plate46, the resilient buffer 60 effects additional noise reduction. Theresilient washers 62 further isolate the lower plate from the effect ofthis impact by absorbing the rebound energy that is released from thebuffer 60 when the gas force on the lower deflector 55 diminishes. Theheads of bolts 61 may be thought of as stops for limiting this reboundmotion and the resilient washers 62 may be thought of as being disposedbetween stops and the deflector 55. V

The inner cylinder 65 is of a thick-walled construction so that itforms, together with the end walls 45, 46 at its opposite ends, athick-walled housing. Because this housing is of a thick-walledconstruction, it is capable of confining within its interior much of thenoise generated upstream therefrom and of thus impeding the transmissionof such noise to the surrounding atmosphere.

To avoid detracting unduly from this noise-confining ability of thethick-walled construction and for other reasons soon to be explained,the number of openings 75 provided in the cylinder 65 is limited, atleast in comparison to the number of openings provided in cylinder 66.The openings 75 that are provided, however, are distributed oversubstantially the entire periphery and length of the cylinder 65.

The exhaust gases pass radially outward through these openings 75,undergoing a generally isentropic expansion that results in a reductionin temperature. Thereafter, the exhaust gases enter the acoustic chamber70, which has a further noise attenuating effect upon the gases.Subsequently, the gases pass through the second or intermediateperforated cylinder 66. Again a decrease in temperature results due toan isentropic expansion as the exhaust gases pass through theperforations 76 of the second cylinder 66. The acoustic chamber 70serves the additional purpose of further dispersing the gas anddistributing the pressure more uniformly over the entire surface area ofthe intermediate cylinder, 66 so that a generally uniform distributionof flow is effected through the openings in cylinder 66. It is to benoted that the intermediate cylinder 66 has more openings therethroughthan theinner cylinder 65, and this contributes to a desirable reductionin the gas velocity through the openings 76 and to a more uniform rateof flow through the openings 76. Both of these factors help to lessenthe amount of noise resulting from the passage of gas through theopenings 76.

Insofar as permitted by manufacturing and mechanical strengthconsiderations, it is desirable that the effective exhaust area throughthe cylinder 66 should be provided by perforations as close together aspossible and as small as possible. This appears to result in acancellation of fiow'turbulence in the exhaust gases, which effects areduced noise level. More specifically, noise is generated by jets ofexhaust gases shearing still air about the periphery of each perforationand the periphery of each related jet. Having the perforations closetogether counteracts such noise generation by eliminating this still airor at least reducing it and thus reducing the effect of the jetsshearing still air. In some cases, it might be desirable to place anintermediate cylinder between the cylinders 65 and 66, and these sameconsiderations would apply to such an intermediate cylinder.

After leaving the acoustic chamber 70 through the openings76, theexhaust gases impinge upon the porous cylinder assembly 67 whichcontains the tightly packed copperwool 79 or a similar substance toprovide further diffusion of the exhaust gases and to attenuate flownoises that may have escaped through the prior components of. them'ufiler assembly. This attenuation is maximized when thecompactedfiller 79 of copper or similar substance isdensely packed between thereticulated elements or screens 77 and 7 8. The surface of the copperWool adjacent to the perforated intermediate cylinder 66 becomespocketed by the impinging jets of exhaust gases passing through'theperforations 76 of the intermediate cylinder. These pockets, not shown,contribute to reduction of the noise level of the escaping exhaustgases.

As previously stated, in the form of the invention being described, anexterior porous cylinder 68 formed from loosely-woven cellulose fibersor a similar porous substance is positioned about the external peripheryof the exhaust muffler assembly 9. This cylinder has been found mostefl'icient in attenuating the higher frequency components of the noise.Further, should the exhaust muffler assembly be exposed to the elements,as previously discussed, a plurality of downwardly-flared louvers suchas shown at 85 may be positioned adjacent to and spaced from theexternal periphery of the muffler assembly 9 to restrict the entry ofmoisture. Eventually, all of the exspare.

5, haust gases are discharged radially outward through the perforationsof the inner cylinder 65.

An important purpose of the deflectors 50 and 55 is to prevent theradial flow through the inner cylinder 65 from being concentrated in anylocalized area of the cylinder, or, in other words, to more uniformlydistribute this radial flow among all of the perforations 75 in thecylinder 65. By providing for a more uniform distribution of this radialflow, the velocity of the gas in traveling through the radially-outerportion of the mufi ler in any given area can be limited to a value lowenough to prevent the generation of excessive noise. Generally speaking,the greater the velocity through a given perforation or opening, thegreater will be the amount of noise generated.

The deflectors perform this important purpose by effecting a moreuniformdistribution of the pressure Within the internal space of the mufllerand also by causing the exhaust gases to flow generally parallel to theinner surface of the cylinder 65 prior to being dischargedradiallyoutward through the perforations 75. This pattern of flow hasbeen found to contribute materially to effecting a more uniformdistribution of radial flow throughout the entire perforated surf-acearea of the inner cylinder 65.

For example, in tests made without the lower deflector 55, it was foundthat there was an excessive concentration of flow through thoseapertures 75 located near the bottom of the cylinder 65. This excessiveflow through the apertures 75 near the bot-tom of the cylinder 65 tendsto cause the gas flowing through the outer portion of the mufiier in theregion adjacent its bottom to travel at an excessive velocity thatgenerates excessive noise.

By cooling the exhaust gases discharged from the circuit breaker, themufiier serves the additional functions of suppressing the ejection offlames from the circuit breaker and of preventing possible flashoversthat could occur if hot ionized gases are permitted to enter regions ofhigh dielectric stress.

Another principle involved in the operation of our muffler is thatwe-transiently store a certain amount of gas Within the cylinder 65while the blast valve 38 is open and thus prolong the discharge throughthe mufiier over a longer period than would occur in the absence of suchstorage. The desire to store some of this gas on a transient basis isanother factor accounting for our limiting the number of openingsprovided in the inner cylinder 65. By prolonging the discharge over alonger period of time than the time that the blast valve is open, we candischarge the gas through the openings in the muffler more slowly. Theslower this discharge, the less noisy it will be. But there are certainlimitations which must be observed. One of these is that the gasesmustbe removed quickly enough to prevent an objectionably high backpressurefrom building up during the interrupting operation. Such back-pressurescould impede the [gas blast in its flow through the arcing region andthis could impair the interrupting ability of the circuit breaker. Theopenings in the cylinder 65, and in the remainder of the enclosure, asWell, are therefore designed to permit rapid enough escape to retard andlimit the pressure buildup sufficiently to permit interruption to becompleted Without any significant impairment of the arc-extinguishingefiiciency of the blast. Another limitation is that the gases must beremoved quickly enough to permit the circuit breaker to operate two ormore times in close succession without impairing the arc-extinguishingefli ciency of the blast. Our mufiler is capable of meeting this latterlimitation since it allows the gases to escape quicktly enough to reducethe pressure within the chamber 69 to atmosphere within about six orseven cycles of 60 cycle alternating cdrrent after the blast valve 38 isfirst opened. The shortest reclosing times ordinarily utilized inpresent-day practice are around twelve to fifteen cycles, so it will beapparent that the muflier completely dissipates the exhaust gases withan ample margin to Enough holes must be present in the cylinder 65 7 toenable this latter performance requirement to be met.

As a further aid in limiting the pressure build-up within the cylinder65, in order to prevent objectionable back pressures from developing,provision is made for cooling the gases while they are transientlystored within the cylinder 65. This cooling reduces the pressure ofstored gas, thus lessening the back pressure effect. This cooling isachieved by forming the deflectors 50' and 55 of a metal capable ofabsorbing a relatively large amount of heat in a short time. Preferably,this material is copper or a copper alloy having a good thermalconductivity, for example, substantially higher than that of steel oriron. Also, the exposed surfaces of the deflectors are preferably leftin a roughened condition to facilitate heat transfer to the deflectors.In certain cases, it may be desirable to locate a suitable heatexchanger (not shown) inside the chamber =69 to further (facilitatecooling of the exhaust gas.

By causing our flow to be distributed generally uniformly throughout allthe openings in a given cylinder, we are able to use a near-minimumnumber of holes of a given size without causing excessive flow throughany of the holes. This enables us to use less holes than would otherwisebe required, thus enabling us to reduce the diameter and length of thecylinders 65-63 forming the muffler enclosure. This, of course, resultsin a highly compact mufl'ler.

As will be evident from the foregoing description certain aspects of theinvention are not limited to the particular details of constructionillustrated, and it is contemplated that other modifications andapplications will occur to those skilled in the art. It is, there-fore,intended that the appended claims shall cover such modifications andapplications that do not depart from the true spirit and scope of theinvention.

What we claim as new and desire to secure by Letters Patent Of theUnited States is:

1. 'In a gas blast circuit breaker having an exhaust passage throughwhich pressurized gases are exhausted after flowing through the arcingregion of the circuit breaker, a noise-reducing exhaust muiflercomprising a pair of end walls and a hollow enclosure extending axiallyof the muffler between said end walls to define an expansion chamberinternally thereof, said enclosure having perforations extendinggenerally radially therethrou-gh at spaced-apart locations about a majorportion of the periphery and length of said enclosure for allowingexhaust gases to flow generally radially outward therethrough, an inletto the expansion chamber in one of said end walls adapted to communicatewith said exhaust passage for directing exhaust gases axially of themufller toward said other end 1 wall, means including opposed deflectormembers adjacent to each end wall for causing exhaust gases from saidinlet to flow repetitively over a circulating path which extends betweensaid two deflectors and has a portion extending generally parallel tothe inner surface of said axially-extending enclosure in the region ofsaid enclosure, whereby to provide for a more uniform distribution offlow through said perforations, said enclosure comprising a plurality ofradiallyspaced generally concentric cylinders extending between said endwalls, each of said cylinders containing perforations through whichexhaust gases from said chamber can flow. a

2. In a gas blast circuit breaker having an exhaust passage throughwhich pressurized gases are exhausted after flowing through the arcingregion of the circuit breaker, a noise-reducing exhaust mufllercomprising a pair of end walls and a hollow enclosure extending ax-;ially of the muffler between said end walls to define an expansionchamber internally thereof, said enclosure having perforations extendinggenerally radially therethrough at spaced-apart locations about a majorportion of the periphery and length of vsaid enclosure for allowing ex-8 V haust gases to flow generally radially outward therethrough, aninlet to the expansion chamber in one of said end walls adapted tocommunicate with said exhaust passage for directing exhaust gasesaxially of the muffler toward said other end wall, meansincludingopposed deflector members adjacent to each end wall for causingexhaust gases from said inlet to flow repetitively, over a circulatingpath which extends between said two deflectors and has a portionextending generally parallel to the inner surface of saidaxially-extending enclosure in the region of said enclosure, whereby toprovide for a more uniform distribution of flow through saidperforations, said enclosure comprising a plurality of radiallyspacedgenerally concentric cylinders extending between said end walls, each ofsaid cylinders containing perforations through which exhaust gases fromsaid chamber can flow, and an additional cylinder positioned about theoutermost one of said perforated cylinders, said additional cylinderbeing of a porous construction that allows ex-v haust gases to escapetherethrough.

3. In a gas blast circuit breaker having an exhaust passage throughwhich pressurized gases are exhausted after flowing through the arcingregion of the circuit breaker, a noise-reducing exhaust mufflercomprising a pair of end walls and a hollow enclosure extending axiallyof the muffler between said end walls to define an expansion chamberinternally thereof, said enclosure having perforations extendinggenerally radially theret-hrough at spaced-apart locations about a majorportion of the periphery and length of said enclosure for allowingexhaust gases to flow generally radially outward therethrough, an inletto the expansion chamber in one of said end Walls adapted to communicatewith said exhaust passage for directing exhaust gases axially of themufiler toward said other end wall, means including opposed deflectormembers adjacent to each end Wall for causing exhaust gases from saidinlet to flow repetitively over a circulating path which extends betweensaid two deflectors and has a portion extending generally parallel tothe inner surface of said axially-extending enclosure in the region ofsaid enclosure, whereby to provide for a more uniform distribution offlow through said perforations, said enclosure comp-rising a pluralityof radiallyspaced generally concentric cylinders extending between saidend walls, each of said cylinders containing perforations through whichexhaust gases from said chamber can flow, and an additional cylinderpositioned about the outermost one of said perforated cylinders, saidadditional cylinder being of a porous construction that allows exhaustgases to escape therethrough, said addi tional cylinder comprising,generally concentrically-positioned, radially-spaced reticulatedcylinders and a quantity of compacted porous material disposed in thespace between said reticulated cylinders.

4. In a gas blast circuit breaker having an exhaust passage throughwhich pressurized gases are exhausted after flowing through the arcingregion of the circuit breaker, a noise-reducing exhaust mufllercomprising a pair of end walls and a hollow enclosure extending axiallyof the muffler between said end walls to define an expansion chamberinternally thereof, said enclosure having perforations extendinggenerally radially theret-hrough at spaced-apart locations about a majorportion of the periphery and length of said enclosure for allowing exhaust gases to flow generally radially outward therethrough, an inlet tothe expansion chamber in one of said end walls adapted to communicatewith said exhaust passage for directing exhaust gases axially of themuffler toward said other end wall, means including opposed deflectormembers adjacent to each end wall for causing exhaust gases from saidinlet to flow repetitively over a circulating path which extends betweensaid two deflectors and has a portion extending generally parallel tothe inner surface of said axially-extending enclosure in the region ofsaid enclosure, whereby to provide for a more uniform distribution offlow through said perforations, said enclosure comprising a cylinderhaving spacedapart perforations through which jets of exhaust gasdischarge radially outward, and an additional cylinder surrounding saidfirst cylinder, said additional cylinder comprising a portion formed ofa densely-packed metallic wool into which said gas jets discharge andform pockets.

5. The structure of claim 4 in combination with still another cylinderof non-metallic porous material surrounding the other cylinders forattenuating high frequency noise components.

6. In a gas blast circuit breaker having an exhaust passage throughwhich pressurized gases are exhausted after flowing through the arcingregion of the circuit breaker, a noise-reducing exhaust mufiiercomprising a pair of end walls and a hollow enclosure extending axiallyof the mufller between said end walls to define an expansion chamberinternally thereof, said enclosure having perforations extendinggenerally radially therethrough at spaced-apart locations about a majorportion of the periphery and length of said enclosure for allowingexhaust gases to fiow generally radially outwardly therethrough, aninlet to the expansion chamber in one of said end walls adapted tocommunicate with said exhaust passage for directing exhaust gasesaxially of the mufller toward said other end wall, means including adeflector on said other end wall for causing gases from said inlet toflow in a reverse axial direction along the internal wall of saidenclosure a-fiter impinging against said deflector, whereby to providefor a more uniform distribution of flow through said perforations, and a10 resilient buffer disposed between said deflector and said other endwall for absorbing a portion of the impact resulting from the exhaustgases striking said deflector.

7. The structure oi. claim 6 in combination with a stop for limitingrebound motion of said deflector away from said other end wall when theforce exerted by said exhaust 'gases diminishes, and second resilientbuffer means between said stop and said deflector plate for absorbingthe energy of said rebound motion.

8. The structure of claim 1 in which said perforations are suflicient innumber and size to limit the pressure within said mufller to a levelthat does not substantially impair the arc-extinguishing ability of saidpressurized gases as compared to a corresponding breaker without saidmufller.

9. The structure of claim 1 in which at least one of said deflectors ismade of a metallic material having a thermal conductivity substantiallygreater than that of steel so as to effectively reduce'the pressurewithin said expansion chamber by cooling.

References Cited in the file of this patent UNITED STATES PATENTS1,045,419 Matula Nov. 26, 1912 2,125,525 Thommen Aug. 2, 1938 2,459,600Strorn Jan. 18, 1949 2,636,961 Schneider Apr. 28, 1953 2,807,329Caldwell Sept. 24, 1957 FOREIGN PATENTS 914,756 France June 24, 1946

1. IN A GAS BLAST CIRCUIT BREAKER HAVING AN EXHAUST PASSAGE THROUGHWHICH PRESSURIZED GASES ARE EXHAUSTED AFTER FLOWING THROUGH THE ARCINGREGION OF THE CIRCUIT BREAKER, A NOISE-REDUCING EXHAUST MUFFLERCOMPRISING A PAIR OF END WALLS AND A HOLLOW ENCLOSURE EXTENDING AXIALLYOF THE MUFFLER BETWEEN SAID END WALLS TO DEFINE AN EXPANSION CHAMBERINTERNALLY THEREOF, SAID ENCLOSURE HAVING PERFORATIONS EXTENDINGGENERALLY RADIALLY THERETHROUGH AT SPACED-APART LOCATIONS ABOUT A MAJORPORTION OF THE PERIPHERY AND LENGTH OF SAID ENCLOSURE FOR ALLOWINGEXHAUST GASES TO FLOW GENERALLY RADIALLY OUTWARD THERETHROUGH, AN INLETTO THE EXPANSION CHAMBER IN ONE OF SAID END WALLS ADAPTED TO COMMUNICATEWITH SAID EXHAUST PASSAGE FOR DIRECTING EXHAUST GASES AXIALLY OF THEMUFFLER TOWARD SAID OTHER END WALL, MEANS INCLUDING OPPOSED DEFLECTORMEMBERS ADJACENT TO EACH END WALL FOR CAUSING EXHAUST GASES FROM SAIDINLET TO FLOW REPETITIVELY OVER A CIRCULATING PATH WHICH EXTENDS BETWEENSAID TWO DEFLECTORS AND HAS A PORTION EXTENDING GENERALLY PARALLEL TOTHE INNER SURFACE OF SAID AXIALLY-EXTENDING ENCLOSURE IN THE REGION OFSAID ENCLOSURE, WHEREBY TO PROVIDE FOR A MORE UNIFORM DISTRIBUTION OFFLOW THROUGH SAID PERFORATIONS, SAID ENCLOSURE COMPRISING A PLURALITY OFRADIALLYSPACED GENERALLY CONCENTRIC CYLINDERS EXTENDING BETWEEN SAID ENDWALLS, EACH OF SAID CYLINDERS CONTAINING PERFORATIONS THROUGH WHICHEXHAUST GASES FROM SAID CHAMBER CAN FLOW.